Ever since recordings of sound began there has been a concerted effort to perfect not only the recording but also the reproduction of the recorded sound. There are numerous ways in which the recorded sound can be changed prior to the sound reaching a listener. It is not our intention here to enumerate all the ways in which distortion of the recorded sound can occur. Suffice to say that over the years advances in technology, especially digital recording and digital processing of sound, has helped reduce or eliminate distortions in the recorded sound prior to the data signal being sent to the speakers. Our concern here is directed to the design of speaker enclosures as one of the last remaining significant sources of distortion in sound reproduction.
Traditionally speaker enclosures were constructed as a hollow wooden (often MDF) box, with a cut-out in the front of the box into which the speaker driver (referred to the speaker henceforth) was mounted. The box typically had a rectangular cuboid shape with sharp edges both inside the hollow cavity of the enclosure and on the outer surface of the enclosure.
It was quickly realised that sharp edges within and around the speaker enclosure could produce distortion to the sound being broadcast due to diffraction of the sound wave around the edge. It was also apparent that the parallel sides of these enclosures could lead to standing waves being created inside the enclosure. These standing waves take energy to create, and therefore a reduction of energy in the transmitted sound at the frequency of the standing wave.
Furthermore, a major concern was sound reflected from the inner surfaces of the speaker enclosure: it is well known that the reflected sound wave, which is created by sound transmitted from the back of the speaker, is out of phase with the sound broadcast out the front of the speaker. This can lead to both constructive and destructive interference of the transmitted sound, both creating distortion of the transmitted sound at various locations in front of the speaker. While interference can in principle occur over at any frequency, it is particularly noticeable at low (bass) frequencies.
Finally; mechanical vibration induced by the motion and inertia of the speaker cone is transmitted and amplified where the reproduced frequencies stimulate, align or interact with the resonant frequencies of the enclosure structure or cavity. The resulting amplified frequencies can be of a magnitude such that they interfere with the sound being projected by the speaker, thus introducing distortion into the reproduced sound.
It is well known in the art that an ideal mounting, especially for a low-frequency speaker, would consist of a large, rigid panel—ideally infinite in size with an infinite space behind the panel to remove reflection of out of phase sound emitted from the rear of the speaker. Clearly such a mounting is not practical, especially in a domestic setting. In a domestic setting there is generally a requirement that the speaker has some aesthetic appeal as well as being limited in size so as not to dominate a room. Furthermore, it is known that the enclosure needs to be rigid without being overly heavy, and be constructed in such a manner as to reduce or eliminate distortion of the frequencies emitted from the speakers by unwanted sound generated within or around the speaker enclosure.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
Throughout this specification, the word “comprise”, or variations thereof such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.